55,629 research outputs found
Cross-polarized common-path temporal interferometry for high-sensitivity strong-field ionization measurements
Absolute density measurements of low-ionization-degree or low-density plasmas ionized by lasers are very important for understanding strong-field physics, atmospheric propagation of intense laser pulses, Lidar etc. A cross-polarized common-path temporal interferometer using balanced detection was developed for measuring plasma density with a sensitivity of ∼0.6 mrad, equivalent to a plasma density-length product of ∼2.6 × 1013 cm-2 if using an 800 nm probe laser. By using this interferometer, we have investigated strong-field ionization yield versus intensity for various noble gases (Ar, Kr, and Xe) using 800 nm, 55 fs laser pulses with both linear (LP) and circular (CP) polarization. The experimental results were compared to the theoretical models of Ammosov-Delone-Krainov (ADK) and Perelomov-Popov-Terent'ev (PPT). We find that the measured phase change induced by plasma formation can be explained by the ADK theory in the adiabatic tunneling ionization regime, while PPT model can be applied to all different regimes. We have also measured the photoionization and fractional photodissociation of molecular (MO) hydrogen. By comparing our experimental results with PPT and MO-PPT models, we have determined the likely ionization pathways when using three different pump laser wavelengths of 800 nm, 400 nm, and 267 nm
Propagation and Structure of Planar Streamer Fronts
Streamers often constitute the first stage of dielectric breakdown in strong
electric fields: a nonlinear ionization wave transforms a non-ionized medium
into a weakly ionized nonequilibrium plasma. New understanding of this old
phenomenon can be gained through modern concepts of (interfacial) pattern
formation. As a first step towards an effective interface description, we
determine the front width, solve the selection problem for planar fronts and
calculate their properties. Our results are in good agreement with many
features of recent three-dimensional numerical simulations.
In the present long paper, you find the physics of the model and the
interfacial approach further explained. As a first ingredient of this approach,
we here analyze planar fronts, their profile and velocity. We encounter a
selection problem, recall some knowledge about such problems and apply it to
planar streamer fronts. We make analytical predictions on the selected front
profile and velocity and confirm them numerically.
(abbreviated abstract)Comment: 23 pages, revtex, 14 ps file
Adiabatic Floquet model for the optical response in femtosecond filaments
The standard model of femtosecond filamentation is based on phenomenological
assumptions which suggest that the ionization-induced carriers can be treated
as free according to the Drude model, while the nonlinear response of the bound
carriers follows the all-optical Kerr effect. Here, we demonstrate that the
additional plasma generated at a multiphoton resonance dominates the saturation
of the nonlinear refractive index. Since resonances are not captured by the
standard model, we propose a modification of the latter in which ionization
enhancements can be accounted for by an ionization rate obtained from
non-Hermitian Floquet theory. In the adiabatic regime of long pulse envelopes,
this augmented standard model is in excellent agreement with direct quantum
mechanical simulations. Since our proposal maintains the structure of the
standard model, it can be easily incorporated into existing codes of filament
simulation.Comment: 14 pages, 6 figures, submitted to New Journal of Physic
Laser pulse propagation in a meter scale rubidium vapor/plasma cell in AWAKE experiment
We present the results of numerical studies of laser pulse propagating in a
3.5 cm Rb vapor cell in the linear dispersion regime by using a 1D model and a
2D code that has been modified for our special case. The 2D simulation finally
aimed at finding laser beam parameters suitable to make the Rb vapor fully
ionized to obtain a uniform, 10 m-long, at least 1 mm in radius plasma in the
next step for the AWAKE experiment.Comment: Conference proceeding ,NIMA_EAAC 2015, 6 pages, 7 figure
Interaction of intense vuv radiation with large xenon clusters
The interaction of atomic clusters with short, intense pulses of laser light
to form extremely hot, dense plasmas has attracted extensive experimental and
theoretical interest. The high density of atoms within the cluster greatly
enhances the atom--laser interaction, while the finite size of the cluster
prevents energy from escaping the interaction region. Recent technological
advances have allowed experiments to probe the laser--cluster interaction at
very high photon energies, with interactions much stronger than suggested by
theories for lower photon energies. We present a model of the laser--cluster
interaction which uses non-perturbative R-matrix techniques to calculate
inverse bremsstrahlung and photoionization cross sections for Herman-Skillman
atomic potentials. We describe the evolution of the cluster under the influence
of the processes of inverse bremsstrahlung heating, photoionization,
collisional ionization and recombination, and expansion of the cluster. We
compare charge state distribution, charge state ejection energies, and total
energy absorbed with the Hamburg experiment of Wabnitz {\em et al.} [Nature
{\bf 420}, 482 (2002)] and ejected electron spectra with Laarmann {\em et al.}
[Phys. Rev. Lett. {\bf 95}, 063402 (2005)]
Ion stopping in dense plasma target for high energy density physics
The basic physics of nonrelativistic and electromagnetic ion stopping in hot and ionized plasma targets is thoroughly updated. Corresponding projectile-target interactions involve enhanced projectile ionization and coupling with target free electrons leading to significantly larger energy losses in hot targets when contrasted to their cold homologues. Standard stoppping formalism is framed around the most economical extrapolation of high velocity stopping in cold matter. Further elaborations pay attention to target electron coupling and nonlinearities due to enhanced projectile charge state, as well. Scaling rules are then used to optimize the enhanced stopping of MeV/amu ions in plasmas with electron linear densities nel ~ 10 18 -10 20 cm -2 . The synchronous firing of dense and strongly ionized plasmas with the time structure of bunched and energetic multicharged ion beam then allow to probe, for the first time, the long searched enhanced plasma stopping and projectile charge at target exit. Laser ablated plasmas (SPQR1) and dense linear plasma columns (SPQR2) show up as targets of choice in providing accurate and on line measurements of plasma parameters. Corresponding stopping results are of a central significance in asserting the validity of intense ion beam scenarios for driving thermonuclear pellets. Other applications of note feature thorium induced fission, novel ion sources and specific material processing through low energy ion beams. Last but not least, the given ion beam-plasma target interaction physics is likely to pave a way to the production and diagnostics of warm dense matter (WDM)
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